1. Technical Field
The invention relates to vacuum gauges and, particularly, to an ionization vacuum gauge employed with carbon nanotubes.
2. Description of Related Art
Ionization vacuum gauges have been used for several years. The conventional ionization vacuum gauge includes a cathode, an anode surrounding the cathode, and an ion collector surrounding the anode. The cathode, the anode and the ion collector are separated from one another so as to not to be in direct electrical contact with each other. In operation, electrons emitted from the cathode travel towards and through the anode and eventually are collected by the ion collector. In their travels, electrons may collide with the molecules and atoms of gas in the vacuum system. Thus, ions may be produced, and collected by the ion collector. As is well known, the pressure of the vacuum system can be calculated by the formula P=(1/k)(Iion/Ielectron), wherein k is a constant with the unit of 1/torr and is a parameter of a particular gauge geometry and electrical parameters, Iion is a current of the ion collector, and Ielectron is a current of the anode.
In the process described above, some electrons may collide with the anode when the electrons travel though the anode and cause the anode to emit X rays. A virtual current Ix may be produced when the X ray irradiates the ion collector. The virtual current Ix will produce a virtual pressure Px which will affect the sensitivity of the ionization vacuum gauge. As is well known, the value of Px can be calculated by the formula Px=(1/k)(Ix/Ielectron). And, the pressure of the vacuum system measured by ionization vacuum gauges is Pm, and Pm=P+Px. As such, the greater the value of Ix is, the less sensitive the ionization vacuum gauges have. As is well known, the value of Ix is related to the atomic number of the anode material, and the greater the atomic number of the anode material, the greater the value of Ix. However, the anode material of the conventional ionization vacuum gauge is metal, which has a relatively high atomic number so as that the virtual current Ix may have a greater value. Therefore, the conventional ionization vacuum gauge tends to be unsuitable for high vacuum systems that are sensitive to temperature and/or light and/or that have extremely high vacuum levels.
What is needed, therefore, is an ionization vacuum gauge that has a small value of virtual current and is suitable for being used in the high vacuum systems.
Corresponding reference characters indicate corresponding parts throughout the several views. The exemplifications set out herein illustrate at least one preferred embodiment of the ionization vacuum gauge.